Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4618
Title: Nomads no more: Early juvenile coho salmon migrants contribute to the adult return
Author: T. R. Bennett, P. Roni, Keith P. Denton, M. McHenry, Raymond E. Moses
Publication Year: 2014
Journal: Ecology of Freshwater Fish
Volume: (early view)
Keywords: fall smolt,nomad,life history

The downstream movement of coho salmon fry and parr in the fall, as distinct from the spring migration of smolts, has been well documented across the range of the species. In many cases these fish overwinter in freshwater but they sometimes enter marine waters. It has long been assumed that these latter fish did not survive to return as adults, and were “surplus” to the stream’s carrying capacity. From 2004 – 2010 we PIT tagged 25,981 juvenile coho salmon in three streams in Washington State to determine their movement, survival, and the contribution of various juvenile life histories to the adult escapement. We detected 86 returning adults, of which 32 originated from fall/winter migrants. Half of these fall/winter migrants spent ~1 year in the marine environment, while the other half spent ~2 years. In addition, the median return date for fall/winter migrants was 16 days later than spring migrants. Our results indicated that traditional methods of spring-only smolt enumeration may underestimate juvenile survival and total smolt production, and also overestimate spring smolt to adult return. These are important considerations for coho salmon life cycle models that assume juvenile coho salmon have a fixed life history or use traditional parr to smolt and smolt to adult return rates.


This manuscript documents the contribution of fall age-0 coho migrants to the returning adult population. These migrants spend either one or two years at sea before returning as adults. 

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Theme: Recovery, Rebuilding and Sustainability of Marine and Anadromous Species
Foci: Characterize vital rates and other demographic parameters for key species, and develop and improve methods for predicting risk and viability/sustainability from population dynamics and demographic information.